linux-kernel - Re: RFC: introduce struct ksymbol

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Date:	Wed, 15 Apr 2009 08:31:06 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Joe Perches <joe@...ches.com>, Sam Ravnborg <sam@...nborg.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Zhaolei <zhaolei@...fujitsu.com>,
	Tom Zanussi <tzanussi@...il.com>,
	Li Zefan <lizf@...fujitsu.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: RFC: introduce struct ksymbol


* Pekka Enberg <penberg@...helsinki.fi> wrote:

> Hi Ingo,
> 
> On Wed, Apr 15, 2009 at 8:58 AM, Ingo Molnar <mingo@...e.hu> wrote:
> >
> > (Sam and Rusty Cc:-ed)
> >
> > * Joe Perches <joe@...ches.com> wrote:
> >
> >> On Wed, 2009-04-15 at 02:00 +0200, Frederic Weisbecker wrote:
> >> > arch/blackfin/kernel/traps.c:   symname = kallsyms_lookup(address, &symsize, &offset, &modname, namebuf);
> >> > arch/powerpc/xmon/xmon.c:               name = kallsyms_lookup(pc, &size, &offset, NULL, tmpstr);
> >> > arch/sh/kernel/cpu/sh5/unwind.c:        sym = kallsyms_lookup(pc, NULL, &offset, NULL, namebuf);
> >> > arch/x86/kernel/ftrace.c:       kallsyms_lookup((unsigned long) syscall, NULL, NULL, NULL, str);
> >> > kernel/kprobes.c:               sym = kallsyms_lookup((unsigned long)p->addr, NULL,
> >> > kernel/lockdep.c:       return kallsyms_lookup((unsigned long)key, NULL, NULL, NULL, str);
> >> > kernel/trace/ftrace.c:  kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
> >> > kernel/trace/ftrace.c:  kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
> >> > kernel/trace/ftrace.c:  kallsyms_lookup((unsigned long)rec->ops->func, NULL, NULL, NULL, str);
> >> > kernel/trace/ftrace.c:  kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
> >> > kernel/trace/ftrace.c:  kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
> >> > kernel/trace/ftrace.c:  kallsyms_lookup(rec->ip, NULL, NULL, &modname, str);
> >> > kernel/trace/ftrace.c:  kallsyms_lookup(*ptr, NULL, NULL, NULL, str);
> >> > kernel/trace/trace_functions.c: kallsyms_lookup(ip, NULL, NULL, NULL, str);
> >> > kernel/trace/trace_output.c:    kallsyms_lookup(address, NULL, NULL, NULL, str);
> >>
> >> Perhaps a conversion from
> >>
> >> "char str[KSYM_SYMBOL_LEN]"
> >> to
> >> "struct ksymbol sym"?
> >>
> >> could be useful.
> >>
> >> There are a few places that use a hard coded length of 128
> >> instead of KSYM_SYMBOL_LENGTH that are also converted.
> >>
> >> Compile tested only
> >
> > Why not 'struct ksym'? That name is unused right now, it is shorter
> > and just as descriptive.
> >
> > Regarding the change... dunno. Sam, Rusty - what do you think?
> >
> > Downsides would be loss of awareness of stack footprint impact. A
> > plain struct is easy to slap on, and it's not immediately visible
> > that it carries 128 bytes of weight. It might also be confusing in
> > terms of the nature of the interface - whether it's a pointery
> > object or not.
> >
> > Prior use:
> >
> >        char str[KSYM_SYMBOL_LEN];
> >
> >        kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
> >
> > New use:
> >
> >        struct ksym sym;
> >
> >        kallsyms_lookup(rec->ip, NULL, NULL, NULL, &sym);
> >
> > Dunno.
> 
> The change makes sense to me. Passing a raw char pointer down the 
> call-chain is a buffer overflow waiting to happen and as a matter 
> of fact, we've had bugs in this area before. See commit 
> 9c24624727f6d6c460e45762a408ca5f5b9b8ef2 ("KSYM_SYMBOL_LEN fixes") 
> for an example.

OK.

Albeit i think that particular bug happened due to the ambigious 
namingof KSYM_SYMBOL_LEN versus KSYM_NAME_LEN. Who would have 
thought that there's a difference between the two and that there's a 
'ksym symbol' versus 'ksym name' distinction?

It would be more robust to have just one length (the longer one), 
and maybe have the shorter one as __KSYM_NAME_LEN - for expert use.

	Ingo
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